Is it true that your parents have rights over you if your a girl until you're 21?

No. It's not true.

You become the age of majority when you turn 18....men and women.

Either your mother lied to you about what the cop told her, or the cop lied.

However, there are restrictions that BUSINESSES can impose....for instance, no sales of alcohol to anyone under the age of 21...male or female.....no car rentals until the age of 25....male or female...no gambling, male or female.....etc.....

The idea that a female would be under more restrictions that a male in this country is LUDICROUS.

No that isn't the case. And getting legal information from the police isn't exactly smart. They aren't lawyers and only taught very narrow areas of the law.

Once you are 18 you are and adult and go about your life as you please. But if you live at home your parents can make all the rules they want and you either can follow them or not and accept the punishment or move.

There are some situations where parents would still have some responsibility, like liability if you have an accident while driving their car, but there is no general control or liability after you turn 18. And your sex most certainly doesn't matter.

Pretty much no. Only to a small extent if you are living under their roof. And a VERY small extent

You're an adult at 18.

He's an idiot. You're an adult at 18. Anywhere in the US.

tell the police officer to talk to me.